Hydraulic steering system with a variable flow device

Abstract

An apparatus ( 10 ) for turning steerable wheels ( 12, 14 ) of a vehicle in response to turning of a steering wheel ( 18 ) of the vehicle. The apparatus includes a hydraulic power steering gear, which does not include a rotary valve responsive to a steering input generated by turning of a steering wheel ( 18 ). The hydraulic steering gear includes a first chamber ( 96 ) for holding hydraulic fluid and a second chamber ( 98 ) for holding hydraulic fluid. An increase in fluid pressure in one chamber acts to turn the steerable wheels ( 12, 14 ) of the vehicle in one direction and an increase in fluid pressure in the other chamber acts to turn the steerable wheels ( 12, 14 ) in a direction opposite the one direction. The apparatus ( 10 ) includes a variable flow mechanism ( 50 ) for supplying a flow of hydraulic fluid to the first and second chambers ( 96, 98 ), which flow varies in dependence upon at least one sensed vehicle condition.

1. An apparatus for turning steerable wheels of a vehicle in response to turning of a steering wheel of the vehicle, the apparatus comprising:
 a first mechanism for connection to the steering wheel having a first member connected to a first pivot point of at least one of the steerable wheels, said first member being movable to turn the steerable wheels in response to turning of the steering wheel; 
 a second mechanism having a hydraulic power steering gear and a second member spaced from the first member and connected to a second pivot point of the at least one of the steerable wheels, said steering gear being free of a rotary valve responsive to a steering input generated by turning of the steering wheel, said steering gear including a first chamber for holding hydraulic fluid and a second chamber for holding hydraulic fluid, an increase in fluid pressure in one chamber acting to move the second member to turn the steerable wheels of the vehicle in one direction and an increase in fluid pressure in the other chamber acting to move the second member to turn the steerable wheels in a direction opposite the one direction; and 
 a variable flow mechanism for supplying a flow of hydraulic fluid to the first and second chambers of said hydraulic steering gear, that varies in dependence upon at least one sensed vehicle condition. 
 
     
     
       2. The apparatus of  claim 1  wherein said variable flow mechanism is in fluid communication with said first chamber for supplying the flow of hydraulic fluid to said first chamber in response to the steerable wheels being turned in the one direction. 
     
     
       3. The apparatus of  claim 1  wherein said variable flow mechanism comprises a pump driven by a variable speed electric motor. 
     
     
       4. The apparatus of  claim 1  wherein said sensed vehicle condition is steering column torque. 
     
     
       5. The apparatus of  claim 1  wherein the first member and the second member extend substantially parallel to one another. 
     
     
       6. The apparatus of  claim 1  wherein the first mechanism includes a rack and pinion gear. 
     
     
       7. apparatus of  claim 6  wherein the first member is connected to the rack and one of the steerable wheels. 
     
     
       8. The apparatus of  claim 1  wherein the second member extends through the first and second chambers of the steering gear. 
     
     
       9. An apparatus for turning steerable wheels of a vehicle in response to turning of a steering wheel of the vehicle, the apparatus comprising:
 an electric motor controlled by an electronic control module in response to at least one sensed vehicle condition for providing steering feel to the vehicle operator; 
 a hydraulic steering gear, said hydraulic steering gear including a first chamber for holding hydraulic fluid and a second chamber for holding hydraulic fluid, an increase in fluid pressure in one chamber acting to turn the steerable wheels of the vehicle in one direction and an increase in fluid pressure in the other chamber acting to turn the steerable wheels in a direction opposite the one direction; 
 a variable flow mechanism controllable by said electronic control module for supplying a variable flow of hydraulic fluid to the first and second chambers of said hydraulic steering gear, which flow varies in dependence upon the at least one sensed vehicle condition; and 
 a mechanism for connection to the steering wheel having a first member connected to a first pivot point of at least one of the steerable wheels, said first member being movable to turn the steerable wheels in response to turning of the steering wheel, a second member connected to a second pivot point of the at least one of the steerable wheels, said second member being movable in response to an increase in pressure in one of the first and second chambers to turn the steerable wheels. 
 
     
     
       10. The apparatus of  claim 9  wherein said sensed vehicle condition is vehicle speed. 
     
     
       11. The apparatus of  claim 10  including a vehicle speed sensor for sensing vehicle speed and for providing a vehicle speed signal, and wherein said electronic control module controlling said variable flow mechanism to supply a first flow of hydraulic fluid to the steering gear in response to said vehicle speed sensor sensing a first vehicle speed, said electronic control module controls said variable flow device to supply a second flow of hydraulic fluid to the steering gear that is higher than said first flow in response to said vehicle speed sensor detecting a second vehicle speed that is lower than said first speed. 
     
     
       12. The apparatus of  claim 9  wherein said variable flow mechanism comprises a pump, driven by a variable speed electric motor. 
     
     
       13. The apparatus of  claim 9  wherein said sensed vehicle condition is steering column torque. 
     
     
       14. The apparatus of  claim 9  wherein said variable flow mechanism is in fluid communication with said first chamber for supplying the flow of hydraulic fluid to said first chamber to turn the steerable wheels in the one direction. 
     
     
       15. The apparatus of  claim 14  wherein said variable flow mechanism includes two pumps and variable speed electric motors for driving said pumps, one of said pumps supplying the flow of hydraulic fluid to said first chamber, and other of said pumps supplying hydraulic fluid to said second chamber. 
     
     
       16. The apparatus of  claim 9  further including at least one valve assembly fluidly connected to said first chamber, said second chamber, and said variable flow mechanism, said valve assembly having a first position to place said variable flow mechanism in fluid communication with said first chamber. 
     
     
       17. The apparatus of  claim 16  wherein said valve assembly has a second position to place said variable flow mechanism in fluid communication with said second chamber. 
     
     
       18. The apparatus of  claim 9  wherein said second member is spaced from said first member. 
     
     
       19. An apparatus for turning steerable wheels of a vehicle in response to turning of a steering wheel of the vehicle, the apparatus comprising:
 an electric motor controlled by an electronic control module in response to at least one sensed vehicle condition for providing steering feel to the vehicle operator; 
 a hydraulic steering gear, said hydraulic steering gear including a first chamber for holding hydraulic fluid and a second chamber for holding hydraulic fluid, an increase in fluid pressure in one chamber acting to turn the steerable wheels of the vehicle in one direction and an increase in fluid pressure in the other chamber acting to turn the steerable wheels in a direction opposite the one direction; and 
 a variable flow mechanism controllable by said electronic control module for supplying a variable flow of hydraulic fluid to the first and second chambers of said hydraulic steering gear, which flow varies in dependence upon the at least one sensed vehicle condition, said variable flow mechanism including a first pump supplying the flow of hydraulic fluid to said first chamber and a first variable speed electric motor for driving said first pump, said variable flow mechanism including a second pump supplying the flow of hydraulic fluid to said second chamber and a second variable speed electric motor for driving said second pump. 
 
     
     
       20. The apparatus of  claim 19  wherein said first variable speed motor is actuated to drive said first pump to supply the flow of hydraulic fluid to the first chamber in response to the steerable wheels being turned in the one direction, said second variable speed motor being actuated to drive said second pump to supply the flow of hydraulic fluid to the second chamber in response to the steerable wheels being turned in the direction opposite the one direction.